1. Field of the Invention
The present invention relates to a cylindrical drum for stencil printing. Specifically, it relates to a cylindrical drum for stencil printing which is suitable to the controlling of ink transferability, etc., in a rotary type stencil printing machine.
2. Description of the Prior Art
A stencil printing method has an advantage in that a large amount of printed matters can thereby be obtained more economically in comparison with the costs if done by other printing methods. A rotary type stencil printing machine has been known as a printing machine which is allowed to exert its advantage at a maximum.
The rotary type stencil printing machine has a porous cylindrical drum which rotates around its own axis. A stencil sheet is attached to the outer surface of the porous cylindrical drum; an ink is supplied from the inner surface of the porous cylindrical drum. Such a cylindrical drum generally has a metallic supporting cylinder having numerous small pores, which may be called a porous cylindrical body and a screen layer rolled around the outer surface of the supporting cylinder described above, which directly rolls the screen layer cylindrically around a pair of flanges which is supported by a center rod without using the metallic supporting cylinder described above, and others.
As a screen layer described above, in order to improve the ink transfer quality, a screen layer consisting of polyester fibers having a fine net structure, and a screen multi-layer composed of a lower mesh stainless screen and a higher mesh polyester fiber screen are known (Japanese Patent Publication No. 63-59393 and Japanese Patent Application laid-open No. 3-254986).
However, when the screen layer of a fine net structure is provided to the supporting cylinder, the stitch deviation of the screen occurs easily. As a result, there is a disadvantage in that the small pores in the supporting cylinder appear as a shadow on the printed image. Further, in the case of a screen multi-layer, it was often inconvenient that an ink was retained between the two layers.
Also, in the case of having no supporting cylinder, since an ink supply roller built in the cylindrical drum is brought in direct contact with the screen, there are such problems that the printing ink cannot uniformly be supplied because the stitch deviation of the screen is large, the deflection thereof is easily yielded at the time of the printing operation because the rigidity thereof is short, and that the pressure distribution at the time of printing becomes nonuniform because the surface condition of the screen is not smooth.